This invention relates to a method of making polymer blends using series reactors and a metallocene catalyst. Monomers used by the invention are ethylene, a higher alpha-olefin (propylene most preferred), and optionally, a non-conjugated diene (ethylidene norbornene, i.e., ENB, most preferred). More specifically, this invention relates to making blends of EP (ethylene-propylene) copolymers in which the blend components differ in any of the following characteristics: 1) composition 2) molecular weight, and 3) crystallinity. We use the terminology EP copolymer to also include terpolymers that contain varying amounts of non-conjugated diene. Such terpolymers are commonly known as EPDM.
There are various advantages for making the aforementioned blends. For example, EP (ethylene propylene copolymer) and EPDM (ethylene propylene diene terpolymer) polymers are often used as blends of two or more polymers to obtain optinum polymer properties for a given application. High molecular weight and low molecular weight polymers are blended yielding a broadened molecular weight distribution (MWD) and therefore better processibillity than a narrow MWD polymer with the same average molecular weight. A semicrystalline polymer may be blended with an amorphous polymer to improve the toughness (green strength) of the amorphous component at temperatures below the semicrystalline polymer melting point. Higher green strength polymers are less likely to cold flow and give improved handling characteristics in processing operations such as calendering and extrusion.
One method of making the aforementioned blends is by mixing two different polymers after they have been polymerized to achieve a target set of properties. Such a method is expensive making it much more desirable to make blends by direct polymerization. Blends by direct polymerization are well known in the prior art such as EPDM manufacture with soluble vanadium based Ziegler-Natta catalysts by using reactors in series and making a polymer with different properties in each reactor. Patents which show vanadium in series reactor operation are U.S. Pat. Nos. 3,629,212, 4,016,342, and 4,306,041, all of which are incorporated by reference for purposes of U.S. patent practice.
Although polymer blending may be performed by vanadium based Ziegler-Natta catalysts in series reactors, there are severe limitations on the amount and characteristics of the polymers that can be made in each reactor, especially in the second reactor. Due to economical considerations, the most preferred method of reactor operation is to add catalyst only to the first reactor to minimize the use of the expensive catalyst components. Because of the rapid deactivation rate of the active vanadium species, catalyst concentration is very low in the second reactor in the series and would be even lower in succeeding reactors. As a result, it is very difficult to make more than about 35 wt % of the total polymer in the second reactor. Also, the low catalyst concentration may put limits on the composition or molecular weight of the polymer. To cure this problem, catalyst activators or additional catalyst can be added to the second and later reactors; however, this raises manufacturing costs. Furthermore, vanadium catalysts are limited in their ability to produce polymers containing less than about 35 wt % ethylene since they much more readily polymerize ethylene than propylene or higher alpha-olefins. In addition, soluble vanadium catalysts are incapable of producing copolymers and terpolymers that contain crystallinity due to the presence of long sequences of isotactic polypropylene.
This invention departs from the prior art by providing a process for producing polymer blends in series reactors that cures the problems of prior art processes associated with property limits. Note that the terms xe2x80x9cmulti-stage reactorxe2x80x9d and xe2x80x9cseries reactorxe2x80x9d are used interchangeably herein. By employing metallocene catalysts, which enjoy a long catalyst lifetime, polymer blends can be made that vary in the amount of the components, the composition of the components, and the molecular weight of the components over much wider ranges than obtainable with prior art vanadium catalysts. In particular, it is the objective of this invention to use a series reactor process and produce the following types of blends: a) blends in which the ethylene content of the polymer made in the first and second reactors differ by 3-75 wt % ethylene, and b) blends in which the MWD of the blend is characterized by Mw/Mn =2.5-20 and Mw/Mn for the individual blend components is 1.7-2.5, and c) blends in which both the polymer composition and MWD meet the criteria in items a) and b) above, and d) blends in which one component contains 0 to 20 wt % ethylene, is semicrystalline due to the presence of isotactic propylene sequences in the chain, and has a melting point of 40-160xc2x0 C., and the other component is amorphous, and e) blends in which one component contains 60 to 85 wt % ethylene, is semicrystalline due to the presence of long ethylene sequences in the chain, and has a melting point of 40-120xc2x0 C., and the other component is amorphous.
This series reactor polymer blend is used in the dynamic vulcanization process to provide improved thermoplastic elastomer products.
Polymerization is preferably homogeneous solution polymerization. The catalyst is a cyclopentadienyl metallocene complex which have two Cp ring systems for ligands or monocyclopentadienyl metallocene catalyst. The metallocene complexes are activated with an alumoxane, eg methylalumoxane (MAO) or a non-coordinating anion (NCA) described further below. Optionally, a trialkyl aluminum scavenger may be added to the reactor feed(s) to prevent deactivation of catalyst by poisons. The reactors are preferably liquid filled, continuous flow, stirred tank reactors. The method employs two or more continuous flow, stirred tank reactors in series with two reactors as a preferred embodiment. Solvent and monomers are fed to each reactor, and preferably catalyst is fed only to the first reactor. Reactors are cooled by reactor jackets or cooling coils, autorefrigeration, prechilled feeds or combinations of all three. Autorefrigerated reactor cooling requires the presence of a vapor phase in the reactor. Adiabatic reactors with prechilled feeds are preferred. This gives rise to a temperature difference between reactors which is helpful for controlling polymer molecular weight. Monomers used in the process are ethylene and a C3-C8 higher alpha-olefin. Propylene is the most preferred as a higher alpha-olefin. Monomers may also optionally include a non-conjugated diene in which case ENB (5-ethylidene-2-norbornene) is the most preferred diene. Reactor temperature depends upon the effect of temperature on catalyst deactivation rate and polymer properties. For economic reasons, it is desirable to operate at as high a temperature as possible; however, temperatures should not exceed the point at which the concentration of catalyst in the second reactor is insufficient to make the desired polymer component in the desired amount. Therefore, temperature will be determined by the details of the catalyst system. In general, the first reactor temperature can vary between 0-110xc2x0 C. with 10-90xc2x0 C. preferred and 20-70xc2x0 C. most preferred. Second reactor temperatures will vary from 40-160xc2x0 C. with 50-140xc2x0 C. preferred and 60-120xc2x0 C. most preferred.
When two reactors are used in series, the composition of the polymer made in the first reactor is 0-85 wt % ethylene while the composition of the polymer made in the second reactor polymer is 0-85 wt % ethylene. The average composition of the polymer blend is 6-85 wt % ethylene.
If Mw/Mn for the blend is less than 2.5, then the difference in composition between the polymer produced in the first and second reactors is 3-75% ethylene, preferably 5-60% ethylene, and most preferably, 7-50% ethylene. If Mw/Mn for the blend is equal to or greater than 2.5, then the composition of the blend components can be either the same or different.
In another embodiment, the difference in ethylene content between the two components is such that one is semi-crystalline and the other is amorphous. Semi-crystalline is defined as having a melting point as measured by DSC and a heat of fusion of at least 10 J/g while amorphous is defined as either the absence of a DSC melting point or a heat of fusion of less than 10 J/g. The semicrystalline polymers of this invention generally have melting points of about 40-160xc2x0 C. depending on the polymer composition. DSC measurements are made by the procedure described in the Examples section. Ethylene propylene copolymers are generally amorphous at ethylene contents between 20 and 60 wt % with the catalysts of this invention. If a polymer component with ethylene crystallinity is desired in the blend, this should have in excess of 60 wt % ethylene. On the other hand, if a component is desired with propylene crystallinity, it should have less than about 20 ethylene. Furthermore, in this case, it is necessary to use a catalyst system that is capable of polymerizing propylene stereospecifically. Catalyst systems that produce isotactic propylene sequences are most preferred.
Depending on the crystallinity level of the semi-crystalline component and the composition difference between the components, the two components may be immiscible and form a phase separated mixture following recovery of the product from the reactor. The presence of multiple phases can readily be measured by standard polymer characterization techniques such as light microscopy, electron microscopy, or atomic force microscopy (AFM). Two phase polymer blends often have advantageous properties, and it is a particular objective of this invention to produce such two phase blends by direct polymerization.
When two reactors are used in series, the amount of polymer made in the second reactor is 15-85 wt % of the total polymer made in both reactors, preferably 30-70 wt % of the total polymer made in both reactors.
MWD of the polymers made with metallocene catalysts tends to be narrow (Mw/Mn less than 2.5), and as a result the polymers do not in general have good processing characteristics. It is a particular objective of this invention that the polymers made in the first and second reactors be of sufficiently different molecular weight so that MWD is broadened. Mw/Mn of the final product is preferably 2.5-20.0 and most preferably 3.0-10.0.
Diene content in the polymer can range from 0-15 wt %, preferably from 2-12 wt % and most preferably from 3-10 wt %. Diene levels in the polymer made in each reactor can be the same or different. Copolymer/terpolymer blends can be made by the process of the invention. For example, if diene is added only to the second reactor, a copolymer of ethylene and propylene can be made in the first reactor while a terpolymer of ethylene, propylene, and diene may be made in the second reactor.
A preferred embodiment of the invention is operating series reactors to produce blends in which the composition of the blend components differs by at least 3 wt % ethylene, Mw/Mn for the blend is equal to or greater than 2.5, and one of the blend components is semi-crystalline. Another preferred feature is that the semicrystalline polymer contain isotactic polypropylene crystallinity.
For a blend combining all of the inventive features described above, at a given average ethylene content and molecular weight for the final product, polymer properties will vary depending on the composition and molecular weight of each component. The process of the invention is capable of making blends in which either: a) polymer 1 has higher ethylene content and higher molecular weight than polymer 2, or b) polymer 1 has higher ethylene content and lower molecular weight than polymer 2. Polymer 1 and polymer 2 can be made in either the first or the second reactor.
For terpolymerization, the blends can further be distinguished by the diene level in each component. Typically, it is preferred to have a higher diene content in the lower molecular weight component to give optimal product properties in vulcanized thermoset compounds.
The present invention may be summarized as a method of making a polymer blend by solution polymerization comprising: a) feeding a first set of monomers and a solvent in predetermined proportions to a first reactor, b) adding a metallocene catalyst to the first reactor, c) operating the first reactor to polymerize the first set of monomers to produce an effluent containing a first polymer, d) feeding the effluent of c) to a second reactor, e) feeding a second set of monomers in predetermined proportions to the second reactor with optional additional solvent, f) operating the second reactor to polymerize the second set of monomers to produce a second polymer without introduction any substantial amount of catalyst. Thus, preferably greater than 50 wt % of the total amount of catalyst added to all reactors is added to the first reactor, more preferably greater than 75 wt %, and most preferably 100 wt % of the total amount of catalyst added to all reactors is added to the first reactor. The first and second set of monomers is chosen from a group consisting of ethylene, higher alpha-olefin and non-conjugated diene. The preferred higher alpha-olefin is polypropylene and the preferred non-conjugated diene is chosen from the group consisting of 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene (DCPD), norbornadiene, and 5-vinyl-2-norbornene (VNB), with ENB most preferred.
A non-conjugated diene may be added to the first set of monomers and/or the second set of monomers in an amount so that the diene content in the polymer blend is preferably from 0-15 wt %, more preferably 2-12 wt %, and most preferably 3-10 wt %.
Control of Ethylene Content
Monomer proportions may be controlled to yield various polymer blends with the blend components having different ethylene content. For example, the monomer proportions in the first reactor and the second reactor may be controlled so that the ethylene content of the first and second polymers differs by 3-75 wt %. Additionally, the monomer proportions in the first reactor and the second reactor may be controlled so that the first polymer has 0 to 85 wt % ethylene, the second polymer has 0 to 85 wt % ethylene, and the polymer blend has 6 to 85 wt % ethylene. Preferably, a blend of semi-crystalline and amorphous polymer is achieved by controlling the monomer proportions in the first reactor and the second reactor so that the ethylene content of the first and second polymers differ so that either: a) the first polymer is semi-crystalline and the second polymer is amorphous, or b) the first polymer is amorphous and the second polymer is semi-crystalline.
Control of Molecular Weight Distribution (MWD)
Preferably, molecular weight of the blend components is controlled to produce a polymer product with a broader MWD than that of the individual components. Specifically, the molecular weight of the first or second polymer or both polymers may be controlled by at least one of: a) adding a chain transfer agent to the first or second reactor or both reactors, b) operating the first and second reactors adiabatically with a temperature difference between the reactors. When broadened MWD is desired, preferably, the molecular weight of the first or second polymer or both polymers is controlled so that the first and second polymers have a Mw/Mn of 1.7-2.5 while the polymer blend has a Mw/Mn of 2.5-20. Most preferably, the molecular weight of the first or second polymer or both polymers is controlled so that the first and second polymers have a Mw/Mn of 1.7-2.5 while the polymer blend has a Mw/Mn of 3.0-10.0. When a narrow MWD product is desired for a particular application the molecular weight of the first or second polymer or both polymers is controlled so that the polymer blend has a Mw/Mn of less than 2.5.
When molecular weight distribution is broadened, it is necessary that one component of the blend be a higher molecular weight than another component of the blend. Thus, the molecular weight of the first or second polymer or both polymers is controlled so that either: a) the first polymer has a higher molecular weight than the second polymer or b) the first polymer has a lower molecular weight than the second polymer. The Mw of each component can be in the range of 10,000 to 2,000,000, preferably in the range of 25,000 to 1,000,000, and most preferably in the range of 50,000 to 500,000.
This series of reactor blend polymers can be further dynamically vulcanized to provide thermoplastic vulcanization.
Control of Both Ethylene Content and MWD
It is also possible to jointly control both ethylene content and molecular weight. When molecular weight is controlled to yield a blend where one component is of higher molecular weight than another, it is preferable to control the ethylene content of each component. Thus the monomer proportions in the first reactor and the second reactor may be controlled so that: a) if the first polymer has a higher molecular weight then the first polymer has a higher ethylene content compared to the second polymer, or b) if the first polymer has a lower molecular weight then the first polymer has a lower ethylene content compared to the second polymer. Furthermore, the monomer proportions in the first reactor and the second reactor may be controlled so that: a) if the first polymer has a higher molecular weight, then the first polymer has a lower ethylene content compared to the second polymer, or b) if the first polymer has a lower molecular weight, then the first polymer has a higher ethylene content compared to the second polymer.
As shown by the preceding disclosure, by practicing the process of this invention, polymer blends can be obtained with various combinations of composition distribution breadth, molecular weight distribution breadth, or both together. If polymer blend component molecular weight is controlled to maintain Mw/Mn for the final product at 2.5 or less, it is preferable that the monomer proportions in the first reactor and the second reactor are controlled so that the ethylene content of the first and second polymers differs by 3-75 wt %, more preferably 5-60 wt %, most preferably 7-50% wt %.
Making a Semi-crystalline/Amorphous Blend
Monomer proportions may also be controlled to yield a blend where one component is semi-crystalline while the other is amorphous. Thus, the monomer proportions in the first reactor and the second reactor may be controlled so that one of the polymers chosen from the first polymer or the second polymer contains 0 to 20 wt % ethylene, is semi crystalline due to the presence of isotactic propylene sequences, and has a melting point of 40-160xc2x0 C. while the other polymer is amorphous. Furthermore, the monomer proportions in the first reactor and the second reactor may be controlled so that one of the polymers chosen from the first polymer or the second polymer contains 60 to 85 wt % ethylene, is semi-crystalline due to the presence of long ethylene sequences, and has a melting point of 40-120xc2x0 C. while the other polymer is amorphous. Blends of two semi-crystalline polymers, one with 0-20% ethylene and the other with 60-85% ethylene are also within the scope of this invention. The level of crystallinity and the composition difference between the components may also selected such that the blend components are immiscible and the final product consists of a two phase mixture. It is particularly desirable to have one of the components of the two phase mixture contain crystallinity due to the presence of isotactic propylene sequences. Such two phase blends cannot be produced by the prior art vanadium catalyst systems.
Catalyst and Reactor Operation
Where the catalyst is concerned, it is preferable for economic reasons that substantially all of the catalyst is added to the first reactor. The catalyst components can be fed to this reactor system either separately or premixed. The catalyst (described further below) is a group 4, 5, and 6 metallocene catalyst activated by a methylalumoxane, MAO or a non-coordinating anion NCA and optionally, a scavenging compound. Preferably, the catalyst is chiral and stereorigid. Preferably the catalyst is capable of producing stereo regular polypropylene.
Where reactor temperatures are concerned, it is preferable that the first reactor operates at temperatures between about 0 to 110xc2x0 C. and the second reactor operates between about 40 to 160xc2x0 C. Preferably, the first reactor operates at temperatures between about 10 to 90xc2x0 C. and the second reactor operates between about 50 to 140xc2x0 C. Most preferably the first reactor operates at temperatures between about 20 to 70xc2x0 C. and the second reactor operates between about 60 to 120xc2x0 C. Preferably, reactors are cooled at least in part by feed prechilling and there is a temperature difference between the reactors.
To protect against catalyst deactivation, a scavenger can be added to at least one of the sets of reactor feeds before their respective polymerizations. Preferably the scavenger is trialkyl aluminum.
Where the reactors are concerned, it is preferable that the first and second reactors are continuous flow stirred tank reactors in series. Additionally, it is preferable that the polymerization in the first and second reactors is homogeneous solution polymerization.
The process of the present invention may be performed by any of the well known multi-stage reactor systems. Two suitable systems are disclosed in U.S. Pat. Nos. 4,016,342 and 4,306,041 which are incorporated by reference for U.S. patent practice. Additionally, copending applications Ser. No. 09/260,966 filed on Mar. 4, 1998 U.S. Pat. No. 6,207,756 Mar. 27, 2001 and Ser. No. 60/076,841 filed on Mar. 4, 1998 disclose suitable multistage reactor systems and are incorporated by reference for U.S. patent practice. If desired, more than two reactors can be used in the process of this invention. The process of the present invention is applicable to slurry or solution polymerization but solution polymerization is preferred and is exemplified herein.
Choice of reactor temperature is dependent upon the effect of temperature on catalyst deactivation rate and polymer properties, principally polymer molecular weight. Temperatures should not exceed the point at which the concentration of catalyst in the second reactor is insufficient to make the desired polymer component in the desired amount. This temperature will be a function of the details of the catalyst system. In general, the first reactor temperature can vary between 0-110xc2x0 C. with 10-90xc2x0 C. preferred and 20-70xc2x0 C. most preferred. Second reactor temperatures will vary from 40-160xc2x0 C., with 50-140xc2x0 C. preferred and 60-120xc2x0 C. most preferred. Reactor may be cooled by reactor jackets, cooling coils, auto refrigeration, pre-chilled feeds or combinations of these. Adiabatic reactors with pre-chilled feeds are preferred. This gives rise to a temperature difference between reactors which is helpful for controlling polymer molecular weight.
Residence time is the same or different in each reactor stage as set by reactor volumes and flow rates. Residence time is defined as the average length of time reactants spend within a process vessel. The total residence time, i.e., the total time spent in all reactors is preferably 2-80 minutes and more preferably 5-40 minutes.
Polymer composition is controlled by the amount of monomers fed to each reactor of the train. In a two reactor series, unreacted monomers from the first reactor flow into the second reactor and so the monomers added to the second reactor are just enough to adjust the composition of the feed to the desired level, taking into account the monomer carry over. Depending on reaction conditions in the first reactor (catalyst concentration, temperature, monomer feed rates, etc.) a monomer may be in excess in the reactor outlet relative to the amount required to make a certain composition in the second reactor. Since it is not economically feasible to remove a monomer from the reaction mixture, situations like this should be avoided by adjusting reaction conditions. The amount of polymer made in each reactor depends on numerous reactor operating conditions such as residence time, temperature, catalyst concentration and monomer concentration, but depends most strongly on monomer concentration. Thus, the amount and composition of the polymer made in the second reactor are interdependent to some degree.
Polymer molecular weight is controlled by reactor temperature, monomer concentration, and by the addition of chain transfer agents such as hydrogen. With metallocene catalysts, polymer molecular weight usually declines as reaction temperature increases and as the ethylene content of the polymer decreases. Adiabatic reactor operation in a two reactor series produces a higher temperature in the second reactor than the first thereby facilitating production of the low molecular weight component in the second reactor. Molecular weight in the second reactor can be further reduced and MWD broadened by adding hydrogen to the second reactor. Hydrogen can also be added to the first reactor but because unreacted hydrogen will carry over to the second reactor the molecular weight of both polymer components will be decreased in this situation and the effect of hydrogen on MWD will be much less. High monomer concentration generally increases polymer molecular weight.
Polymer composition may affect polymer molecular weight, other things being equal, due to chain transfer processes involving the alpha-olefin comonomer. In general, it is often observed that molecular weight decreases as the alpha-olefin content of the polymer is raised. In the context of molecular weight control, the alpha-olefin comonomer may be viewed as a chain transfer agent and may be used to affect the molecular weight of one of the blend components.
In a two reactors in series, diene can be added to either or both reactors. Diene is added only to the second reactor to produce a copolymer/terpolymer blend.
The polymer product can be recovered from solution at the completion of the polymerization by any of the techniques well known in the art such as steam stripping followed by extrusion drying or by devolatilizing extrusion.
Higher Alpha-olefins
Although the most preferred higher alpha-olefin is propylene for use with this invention, other higher alpha-olefins may be used as set forth below. Higher alpha-olefins suitable for use may be branched or straight chained, cyclic, and aromatic substituted or unsubstituted, and are preferably C3-C18 alpha-olefins. Illustrative non-limiting examples of preferred higher alpha-olefins are propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 1-dodecene. Mixed alpha-olefins can be used as well as mixed alpha- and non-alpha-olefins (e.g., mixed butenes) as long as any non-polymerizable olefins in the mixture act as inerts towards the catalyst. illustrative of such substituted higher alpha-olefins are compounds of the formula H2Cxe2x95x90CHxe2x80x94CnH2nxe2x80x94X wherein n is an integer from 1 to 30 carbon atoms (preferably to 10 carbon atoms), and X preferably comprises CH3 but can comprise aryl, alkaryl, or cycloalkyl substitutents. Also useful are higher alpha-olefins substituted by one or more such X substituents wherein the substituent(s) are attached to a non-terminal carbon atom, more preferably being attached to a non-terminal carbon atom which is preferably 2 to 30 carbons removed from the terminal carbon atom, with the proviso that the carbon atom so substituted is preferably not in the 1- or 2-carbon position in the olefin. The higher alpha-olefins, when substituted, are preferably not substituted with aromatics or other bulky groups on the 2-carbon position since aromatic and bulky groups interfere with the subsequent desired polymerization.
Diene
Although ENB is the most preferred non-conjugated diene to be used in the invention, other non-conjugated dienes are useful as set forth below. Non-conjugated dienes useful as co-monomers preferably are straight chain, hydrocarbon di-olefins or cycloalkenyl-substituted alkenes, having about 6 to about 15 carbon atoms, for example: (a) straight chain acyclic dienes, such as 1,4-hexadiene and 1,6-octadiene; (b) branched chain acyclic dienes, such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; and 3,7-dimethyl-1,7-octadiene; (c) single ring alicyclic dienes, such as 1,4-cyclohexadiene; 1,5-cyclo-octadiene and 1,7-cyclododecadiene; (d) multi-ring alicyclic fused and bridged ring dienes, such as tetrahydroindene; norbornadiene; methyl-tetrahydroindene; dicyclopentadiene (DCPD); bicyclo-(2.2.1)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes, such as 5-methylene-2-norbornene (MNB), 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene (VNB); (e) cycloalkenyl-substituted alkenes, such as vinyl cyclohexene, allyl cyclohexene, vinyl cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene, and vinyl cyclododecene. Of the non-conjugated dienes typically used, the preferred dienes are dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, and tetracyclo (xcex94-11,12) 5,8 dodecene. Particularly preferred diolefins are 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene (DCPD), norbornadiene, and 5-vinyl-2-norbornene (VNB). Note that throughout this application the terms xe2x80x9cnon-conjugated dienexe2x80x9d and xe2x80x9cdienexe2x80x9d are used interchangeably.
Solvent
Although hexane is the most preferred solvent to be used in the invention, other solvents which may be used are hydrocarbons such as aliphatics, cycloalphatics, and aromatic hydrocarbons with the proviso that the solvent is inert towards the catalyst. Preferred solvents are C12 or lower straight-chain or branched-chain, saturated hydrocarbons, and C5 to C9 saturated alicyclic or aromatic hydrocarbons. Examples of such solvents or reaction media are hexane, butane, pentane, heptane, cyclopentane, cyclohexane, cycloheptane, methyl cyclopentane, methyl cyclohexane, isooctane, benzene, toluene, and xylene. In addition, one or more -olefins, either alone or admixed with other media, may serve as the reaction media, at selected concentrations of such olefins.
Metallocene Catalyst Precursors
The term xe2x80x9cmetallocenexe2x80x9d and xe2x80x9cmetallocene catalyst precursorxe2x80x9d as used herein shall be understood to refer to compounds possessing a transition metal M, with cyclopentadienyl (Cp) ligands, at least one non-cyclopentadienyl-derived ligand X, and zero or one heteroatom-containing ligand Y, the ligands being coordinated to M and corresponding in number to the valence thereof The metallocene catalyst precursors are generally neutral complexes but when activated with a suitable co-catalyst yield an active metallocene catalyst which refers generally to an organometallic complex with a vacant coordination site that can coordinate, insert, and polymerize olefins. The metallocene catalyst precursors is preferably one of, or a mixture of metallocene compounds of either or both of the following types:
1) Cyclopentadienyl (Cp) complexes which have two Cp ring systems for ligands. The Cp ligands form a sandwich complex with the metal and can be free to rotate (unbridged) or locked into a rigid configuration through a bridging group. The Cp ring ligands can be like or unlike, unsubstituted, substituted, or a derivative thereof such as a heterocyclic ring system which may be substituted, and the substitutions can be fused to form other saturated or unsaturated rings systems such as tetrahydroindenyl, indenyl, or fluorenyl ring systems. These cyclopentadienyl complexes have the general formula
(C1R1m)R3n(Cp2R2p)MXq
wherein Cp1 of ligand (Cp1R1m)and Cp2 of ligand (Cp2R2p) are the same or different cyclopentadienyl rings R1 and R2 each is, independently, a halogen or a hydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, m is 0 to 5, p is 0 to 5, and two R1 and/or R2 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated there with can be joined together to form a ring containing from 4 to about 20 carbon atoms, R3 is a bridging group, n is the number of atoms in the direct chain between the two ligands and is 0 to 8, preferably 0 to 3, M is a transition metal having a valence of from 3 to 6, preferably from group 4, 5, or 6 of the periodic table of the elements and is preferably in its highest oxidation state, each X is a non-cyclopentadienyl ligand and is, independently, a halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, q is equal to the valence of M minus 2.
2) Monocyclopentadienyl complexes which have only one Cp ring system as a ligand. The Cp ligand forms a half-sandwich complex with the metal and can be free to rotate (unbridged) or locked into a rigid configuration through a bridging group to a heteroatom-containing ligand. The Cp ring ligand can be unsubstituted, substituted, or a derivative thereof such as a heterocyclic ring system which may be substituted, and the substitutions can be fused to form other saturated or unsaturated rings systems such as tetrahydroindenyl, indenyl, or fluorenyl ring systems. The heteroatom containing, ligand is bound to both the metal and optionally to the Cp ligand through the bridging group. The heteroatom itself is an atom with a coordination number of three from group VA or VIA of the periodic table of the elements. These mono-cyclopentadienyl complexes have the general formula
(Cp1R1m)R3n(YrR2)MXs
wherein R1 is, each independently, a halogen or a hydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, xe2x80x9cmxe2x80x9d is 0 to 5, and two R1 substituents on adjacent carbon atoms of the cyclopentadienyl ring associated there with can be joined together to form a ring containing from 4 to about 20 carbon atoms, R3 is a bridging group, xe2x80x9cnxe2x80x9d is 0 to 3, M is a transition metal having a valence of from 3 to 6, preferably from group 4, 5, or 6 of the periodic table of the elements and is preferably in its highest oxidation state, Y is a heteroatom containing group in which the heteroatom is an element with a coordination number of three from Group VA or a coordination number of two from group VIA preferably nitrogen, phosphorous, oxygen, or sulfur, R2 is a radical selected from a group consisting of C1 to C20 hydrocarbon radicals, substituted C1 to C20 hydrocarbon radicals, wherein one or more hydrogen atoms is replaced with a halogen atom, and when Y is three coordinate and unbridged there may be two R2 groups on Y each independently a radical selected from a group consisting of C1 to C20 hydrocarbon radicals, substituted C1 to C20 hydrocarbon radicals, wherein one or more hydrogen atoms is replaced with a halogen atom, and each X is a non-cyclopentadienyl ligand and is, independently, a halogen or a hydrocarbyl, oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted organometalloid, oxyhydrocarbyl-substituted organometalloid or halocarbyl-substituted organometalloid group containing up to about 20 carbon atoms, xe2x80x9csxe2x80x9d is equal to the valence of M minus 2.
Examples of suitable biscyclopentadienyl metallocenes of the type described in group 1 above for the invention are disclosed in U.S. Pat. Nos. 5,324,800; 5,198,401; 5,278,119; 5,387,568; 5,120,867; 5,017,714; 4,871,705; 4,542,199; 4,752,597; 5,132,262; 5,391,629; 5,243,001; 5,278,264; 5,296,434; and 5,304,614, all of which are incorporated by reference herein.
Illustrative, but not limiting, examples of preferred ciscyclopentadienyl metallocenes of the type described in group 1 above for the invention are the racemic isomers of:
xcexc-(CH3)2Si(indenyl)2M(Cl)2 
xcexc-(CH3)2Si(indenyl)2M(CH3)2 
xcexc-(CH3)2Si(tetrahydroindenyl)2M(Cl)2 
xcexc-(CH3)2Si(tetrahydroindenyl)2M(CH3)2 
xcexc-(CH3)2Si(indenyl)2M(CH2CH3)2 
xcexc-(C6H5)2C(indenyl)2M(CH3)2;
wherein M is chosen from a group consisting of Zr and Hf.
Examples of suitable unsymmetrical cyclopentadienyl metallocenes of the type described in group 1 above for the invention are disclosed in U.S. Pat. Nos. 4,892,851; 5,334,677; 5,416,228; and 5,449,651; and are described in publication J. Am. Chem. Soc. 1988, 110, 6255, all of which are incorporated by reference herein.
Illustrative, but not limiting, examples of preferred unsymmetrical cyclopentadienyl metallocenes of the type described in group 1 above for the invention are:
xcexc-(C6H5)2C(cyclopentadienyl)(fluorenyl)M(R)2 
xcexc-(C6H5)2C(3-methylcyclopentadienyl)(fluorenyl)M(R)2 
xcexc-(CH3)2C(cyclopentadienyl)(fluorenyl)M(R)2 
xcexc-(C6H5)2C(cyclopentadienyl)(2-methylindenyl)M(CH3)2 
xcexc-(C6H5)2C(3-methylcyclopentadienyl)(2-methylindenyl)M(Cl)2 
xcexc-(C6H5)2C(cyclopentadienyl)(2,7-dimethylfluorenyl)M(R)2 
xcexc-(CH3)2C(cyclopentadienyl)(2,7-dimethylfluorenyl)M(R)2;
wherein M is chosen form a group consisting of Zr and Hf, and R is chosen from a group consisting of Cl and CH3.
Examples of suitable monocyclopentadienyl metallocenes of the type described in group 2 above for the invention are disclosed in U.S. Pat. Nos. 5,026,798; 5,057,475; 5,350,723; 5,264,405; 5,055,438 and are described in publication WO 96/002244, all of which are incorporated by reference herein.
Illustrative, but not limiting, examples of preferred monocyclopentadienyl metallocenes of the type described in group 2 above for the invention are:
xcexc-(CH3)2Si(cyclopentadienyl)(1-adamantylamido)M(R)2 
xcexc-(CH3)2Si(3-tertbutylcyclopentadienyl)(1-adamantylamido)M(R)2 
xcexc-(CH2(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)2 
xcexc-(CH3)Si(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)2 
xcexc-(CH3)2C(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)2 
xcexc-(CH3)2Si(tetramethylcyclopentadienyl)(1-tertbutylamido)M(R)2 
xcexc-(CH3)2Si(fluorenyl)(1-tertbutylamido)M(R)2 
xcexc-(CH3)2Si(tetramethylcyclopentadienyl)(1-cyclododecylamido)M(R)2 
xcexc-(C6H5)2C(tetramethylcyclopentadienyl)(1-cyclododecylamido)M(R)2;
wherein M is selected from a group consisting of Ti, Zr, and Hf and wherein R is selected from Cl and CH3.
Another class of organometallic complexes that are useful catalysts for the process describe herein are those with diimido ligand systems such as those described in WO 96/23010 assigned to Du Pont. These catalytic polymerization compounds are incorporated here by reference.
Noncoordinating Anions
The term xe2x80x9cnoncoordinating anionxe2x80x9d (NCA) means an anion which either does not coordinate to said transition metal cation or which is only weakly coordinated to said cation thereby remaining sufficiently labile to be displaced by a neutral Lewis base. xe2x80x9cCompatiblexe2x80x9d noncoordinating anions are those which are not degraded to neutrality when the initially formed complex decomposes. Further, the anion will not transfer an anionic substituent or fragment to the cation so as to cause it to form a neutral four coordinate metallocene compound and a neutral by-product from the anion. Noncoordinating anions useful in accordance with this invention are those which are compatible, stabilize the metallocene cation in the sense of balancing its ionic charge in a +1 state, yet retain sufficient lability to permit displacement by an ethylenically or acetylenically unsaturated monomer during polymerization. Additionally, the anions useful in this invention will be large or bulky in the sense of sufficient molecular size to largely inhibit or prevent neutralization of the metallocene cation by Lewis bases other than the polymerizable monomers that may be present in the polymerization process. Typically the anion will have a molecular size of greater than or equal to about 4 angstroms.
Descriptions of ionic catalysts for coordination polymerization comprised of metallocene cations activated by non-coordinating anions appear in the early work in EP-A-0 277 003, EP-A-0 277 004, U.S. Pat. Nos. 5,198,401 and 5,278,119, and WO92100333. These teach a preferred method of preparation wherein metallocenes (bisCp and monoCp) are protonated by an anionic precursors such that an alkyl/hydride group is abstracted from a transition metal to make it both cationic and charge-balanced by the non-coordinating anion. The use of ionizing ionic compounds not containing an active proton but capable of producing both the active metallocene cation and a noncoordinating anion is also known. See, EP-A-0 426 637, EP-A-0 573 403 and U.S. Pat. No. 5,387,568. Reactive cations other than Bronsted acids capable of ionizing the metallocene compounds include ferrocenium triphenylcarbonium and triethylsilylinium cations. Any metal or metalloid capable of forming a coordination complex which is resistant to degradation by water (or other Bronsted or Lewis Acids) may be used or contained in the anion of the second activator compound. Suitable metals include, but are not limited to, aluminum, gold, platinum and the like. Suitable metalloids include, but are not limited to, boron, phosphorus, silicon and the like. The description of non-coordinating anions and precursors thereto of these documents are incorporated by reference for purposes of U.S. patent practice.
An additional method of making the ionic catalysts uses ionizing anionic pre-cursors which are initially neutral Lewis acids but form the cation and anion upon ionizing reaction with the metallocene compounds, for example tris(pentafluorophenyl) boron acts to abstract an alkyl, hydride or silyl ligand to yield a metallocene cation and stabilizing non-coordinating anion, see EP-A-0 427 697 and EP-A-0 520 732. Ionic catalysts for addition polymerization can also be prepared by oxidation of the metal centers of transition metal compounds by anionic precursors containing metallic oxidizing groups along with the anion groups, see EP-A-0 495 375. The description of non-coordinating anions and precursors thereto of these documents are similarly incorporated by reference for purposes of U.S. patent practice.
Examples of suitable activators capable of ionic cationization of the metallocene compounds of the invention, and consequent stabilization with a resulting noncoordinating anion include:
trialkyl-substituted ammonium salts such as;
triethylammonium tetraphenylborate,
tripropylammonium tetraphenylborate,
tri(n-butyl)ammonium tetraphenylborate,
trimethylammonium tetrakis(p-tolyl)borate,
trimethylammonium tetrakis(o-tolyl)borate,
tributylammonium tetrakis(pentafluorophenyl)borate,
tripropylammonium tetrakis(o,p-dimethylphenyl)borate,
tributylammonium tetrakis(m,m-dimethylphenyl)borate,
tributylammonium tetrakis(p-trifluoromethylphenyl)borate,
tributylammonium tetrakis(pentafluorophenyl)borate,
tri(n-butyl)ammonium tetrakis(o-tolyl)borate and the like;
N,N-dialkyl anilinium salts such as;
N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate,
N,N-dimethylanilinium tetrakis(heptafluoronaphthyl)borate,
N,N-dimethylanilinium tetrakis(perfluoro-4-biphenyl)borate,
N,N-dimethylanilinium tetraphenylborate,
N,N-diethylanilinium tetraphenylborate,
N,N-2,4,6-pentamethylanilinium tetraphenylborate and the like;
dialkyl ammonium salts such as;
di-(isopropyl)ammonium tetrakis(pentafluorophenyl)borate,
dicyclohexylammonium tetraphenylborate and the like;
and triaryl phosphonium salts such as;
triphenylphosphonium tetraphenylborate,
tri(methylphenyl)phosphonium tetraphenylborate,
tri(dimethylphenyl)phosphonium tetraphenylborate and the like.
Further examples of suitable anionic precursors include those comprising a stable carbonium ion, and a compatible non-coordinating anion. These include; tropillium tetrakis(pentafluorophenyl)borate,
triphenylmethylium tetrakis(pentafluorophenyl)borate,
benzene(diazonium)tetrakis(pentafluorophenyl)borate,
tropillium phenyltris(pentafluorophenyl)borate,
triphenylmethylium phenyl-(trispentafluorophenyl)borate,
benzene(diazonium)phenyl-tris(pentafluorophenyl)borate,
tropillium tetrakis(2,3,5,6-tetrafluorophenyl)borate,
triphenylmethylium tetrakis(2,3,5,6-tetrafluorophenyl)borate,
benzene(diazonium) tetrakis(3,4,5-trifluorophenyl)borate,
tropillium tetrakis(3,4,5-trifluorophenyl)borate,
benzene(diazonium)tetrakis(3,4,5-trifluorophenyl)borate,
tropillium tetrakis(3,4,5-trifluorophenyl)aluminate,
triphenylmethylium tetrakis(3,4,5-trifluorophenyl)aluminate,
benzene(diazonium)tetrakis(3,4,5-trifluorophenyl)aluminate,
tropillinum tetrakis(3,2,2-trifluoroethenyl)borate,
triphenylmethylium tetrakis(3,2,2-trifluoroethenyl)borate,
benzene(diazonium)tetrakis(3,2,2-trifluoroethenyl)borate,
tropillium tetrakis(2,3,4,5-tetrafluorophenyl)borate,
triphenylmethylium tetrakis(2,3,4,5-tetrafluorophenyl)borate,
benzene(diazonium)tetrakis(2,3,4,5-tetrafluorophenyl)borate, and the like.
Where the metal ligands include halide moieties for example, (methyl-phenyl)silylene(tetra-methyl-cyclopentadienyl)(tert-butyl-amido)zirconium dichloride) which are not capable of ionizing abstraction under standard conditions, they can be converted via known alkylation reactions with organometallic compounds such as lithium or aluminum hydrides or alkyls, alkylalumoxanes, Grignard reagents, etc. See EP-A-0 500 944, EP-A1-0 570 982 and EP-A1-0 612 768 for processes describing the reaction of alkyl aluminum compounds with dihalide substituted metallocene compounds prior to or with the addition of activating anionic compounds. For example, an aluminum alkyl compound may be mixed with the metallocene prior to its introduction into the reaction vessel. Since the alkyl aluminum is also suitable as a scavenger its use in excess of that normally stoichiometrically required for akylation of the metallocene will permit its addition to the reaction solvent with the metallocene compound. Normally alumoxane would not be added with the metallocene so as to avoid premature activation, but can be added directly to the reaction vessel in the presence of the polymerizable monomers when serving as both scavenger and alkylating activator.
Known alkylalumoxanes are additionally suitable as catalyst activators, particularly for those metallocenes comprising halide ligands. The alumoxane component useful as catalyst activator typically is an oligomeric aluminum compound represented by the general formula (Rxe2x80x94Alxe2x80x94O)n, which is a cyclic compound, or R(Rxe2x80x94Alxe2x80x94O)nAIR2, which is a linear compound. In the general alumoxane formula R is a C1 to C5 alkyl radical, for example, methyl, ethyl, propyl, butyl or pentyl and xe2x80x9cnxe2x80x9d is an integer from 1 to about 50. Most preferably, R is methyl and xe2x80x9cnxe2x80x9d is at least 4, i.e. methylalumoxane (MAO). Alumoxanes can be prepared by various procedures known in the art. For example, an aluminum alkyl may be treated with water dissolved in an inert organic solvent, or it may be contacted with a hydrated salt, such as hydrated copper sulfate suspended in an inert organic solvent, to yield an alumoxane. Generally, however prepared, the reaction of an aluminum alkyl with a limited amount of water yields a mixture of the linear and cyclic species of the alumoxane.
Although trialkyl aluminum is the most preferred scavenger to be used in the invention, other scavengers may be used as set forth below. The term xe2x80x9cscavenging compoundsxe2x80x9d as used in this application and in the claims is meant to include those compounds effective for removing polar impurities from the reaction solvent. Such impurities can be inadvertently introduced with any of the polymerization reaction components, particularly with solvent, monomer and comonomer feed, and adversely affect catalyst activity and stability. It can result in decreasing or even elimination of catalytic activity, particularly when a metallocene cation-noncoordinating anion pair is the catalyst system. The polar impurities, or catalyst poisons include water, oxygen, oxygenated hydrocarbons, metal impurities, etc. Preferably, steps are taken before provision of such into the reaction vessel, for example, by chemical treatment or careful separation techniques after or during the synthesis or preparation of the various components, but some minor amounts of scavenging compound will still normally be required in the polymerization process itself Typically the scavenging compound will be an organometallic compound such as the Group-13 organometallic compounds of U.S. Pat. No. 5,153,157, 5,241,025, EP-A-638 and WO-A-91/09882 and WO-A-94/03506, noted above, and that of WO-A-93/14132. Exemplary compounds include triethyl aluminum, triethyl borane, tri-isobutyl aluminum, isobutyl aluminumoxane, those having bulky substituents covalently bound to the metal or metalloid center being preferred to minimize adverse interaction with the active catalyst. When an alumoxane is used as activator, additional scavenging compounds are not necessary. The amount of scavenging agent to be used with metallocene cation-noncoordinating anion pairs is minimized during polymerization reactions to that amount effective to enhance activity.
The metallocene catalyst component and the activator may be fed to the reactor either separately or premixed.
The catalyst systems especially desirable for EP polymerization give a combination of high activity, good incorporation of the alpha-olefin and diene into the chain, and polymer molecular weights high enough for elastomer applications at economically attractive reactor temperatures. Catalyst systems particularly preferred for achieving these objectives include catalysts selected the grom consisting of xcexc-(CH3)2Si(Indenyl)2Hf(CH3)2, xcexc-(CH3)2Si[tetramethylcyclopentadienyl][adamantylamido]Ti(CH3)2, or xcexc-(C6H5)2Si[Cyclopentadienyl][flourenyl]Hf(CH3)2.
Although trialkyl aluminum is the most preferred scavenger to be used in the invention, other scavengers may be used as set forth below. The term xe2x80x9cscavenging compoundsxe2x80x9d as used in this application and in the claims is meant to include those compounds effective for removing polar impurities from the reactor feed mixture. Such impurities can be inadvertently introduced with any of the polymerization reaction components, particularly with solvent and monomer, and adversely affect catalyst activity and stability. It can result in decreasing or even elimination of catalytic activity, particularly when a metallocene cation-noncoordinating anion pair is the catalyst system. The polar impurities, or catalyst poisons include water, oxygen, metal impurities, etc. Preferably, steps are taken before provision of such into the reaction vessel, for example, by chemical treatment or careful separation techniques after or during the synthesis or preparation of the various components, but some minor amounts of scavenging compound will still normally be required in the polymerization process itself Typically the scavenging compound will be an organometallic compound such as the Group-13 organometallic compounds of U.S. Pat. No. 5,153,157, 5,241,025, EP-A-638 and WO-A-91/09882 and WO-A-94/03506, noted above, and that of WO-A-93/14132. Exemplary compounds include triethyl aluminum, triethyl borane, tri-isobutyl aluminum, isobutyl aluminumoxane, those having bulky substituents covalently bound to the metal or metalloid center being preferred to minimize adverse interaction with the active catalyst. When an alumoxane is used as activator, additional scavenging compounds are not necessary. The amount of scavenging agent to be used with metallocene cation-noncoordinating anion pairs is minimized during polymerization reactions to that amount effective to enhance activity.
Dynamic Vulcanization
The rubber components of the series reactor blend is generally present as small, i.e., micro-size particles within a continuous thermoplastic resin matrix, although a co-continuous morphology or a phase inversion is also possible depending upon the amount of rubber relative to plastic. The rubber is desirably at least partially crosslinked, and preferably is completely or fully crosslinked. It is preferred that the rubber be crosslinked by the process of dynamic vulcanization. As used in the specification and claims, the term xe2x80x9cdynamic vulcanizationxe2x80x9d means a vulcanization or curing process for a rubber blended with a thermoplastic resin, wherein the rubber is vulcanized under conditions of shear at a temperature at which the mixture will flow. The rubber is thus simultaneously crosslinked and dispersed as fine particles within the thermoplastic resin matrix, although as noted above, other morphologies may exist. Dynamic vulcanization is effected by mixing the thermoplastic elastomer components at elevated temperatures in conventional mixing equipment such as roll mills, Banbury mixers, Brabender mixers, continuous mixers, mixing extruders, and the like. The unique characteristic of dynamically cured compositions is that, notwithstanding the fact that the rubber component is partially or fully cured, the compositions can be processed and reprocessed by conventional plastic processing techniques such as extrusion, injection molding, and compression molding. Scrap or flashing can be salvaged and reprocessed.
The terms xe2x80x9cfully vulcanizedxe2x80x9d and xe2x80x9cfully curedxe2x80x9d or xe2x80x9cfully crosslinkedxe2x80x9d as used in the specification and claims means that the rubber component to be vulcanized has been cured or crosslinked to a state in which the elastomeric properties of the crosslinked rubber are similar to those of the rubber in its conventional vulcanized state, apart from the thermoplastic elastomer composition.
The degree of cure can be described in terms of gel content, or conversely, extractable components. The rubber component can be described as fully cured when less than about 5% and preferably less than 3%, of the rubber which is capable of being cured by hydrosilylation is extractable from the thermoplastic elastomer product by a solvent for that rubber. Alternatively, the degree of cure may be expressed in terms of crosslink density. All of these descriptions are all known in the art, for example in U.S. Pat. Nos. 5,100,947 and 5,157,081, both of which are fully incorporated herein by this reference.
The compositions can be processed and reprocessed by conventional plastic processing techniques such as extrusion, injection molding, and compression molding. Those of ordinary skill in the art will appreciate the appropriate quantities, types of cure systems, and vulcanization conditions required to carry out the vulcanization of the rubber. The rubber can be vulcanized using varying amounts of curative, varying temperature, and varying time of cure in order to obtain the optimum crosslinking desired. Any known cure system for the rubber can be used, so long as it is suitable under the vulcanization conditions with the specific olefinic rubber or combination of rubbers being used with the polyolefin. These curatives include sulfur, sulfur donors, metal oxides, resin systems, peroxide-based systems, hydrosilation with platinum or peroxide and the like, both with and without accelerators and coagents.